https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108234
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
If I change func to:
template <auto &V> int func(X<V>) { return 1; }
And then clang accepts it.
The question becomes what can be deduced as the type of V.
Here is a slightly different testcase:
```
template <int&> struct X{};
template <typename T>
void ff(){};
template <typename T, T V> int func(X<V>) { return 1; }
int i;
int main() { return func(X<i>{}); }
```
Note GCC rejects the above testcase for C++14 but accepts it for C++17.
So I am not 100% this is invalid and clang just does not implement some rule of
C++17 correctly dealing with reference types ...
